Generally, speech therapists teach their patients with charts, diagrams, written exercises, or recorded sounds which attempt to convey to the patient the proper formation of the tongue and lips to make a particular sound. These methods are often transformed into interesting and workable exercises, stories, and games to be practiced by the patient as a means of correcting speech impediments. This is a long and difficult procedure, partly because of the difficulty of the patients in understanding exectly how the tongue is to be placed and how it is to be manipulated in order to prevent an old habit and to reinforce a new habit which will result in the elimination of a speech impediment. This is an especially difficult area because traditionally the speech therapist can only use words to try and describe the necessary positions, manipulations, and desired results.
It is even more difficult for the extremely young, the deaf, the blind and the retarded than it is for those with normal faculties to understand how to position and manipulate their tongue pursuant to verbal directions. The therapist can indicate correct position of the tongue in her mouth or in the patient's mouth only with the mouth fully open so that the tongue can be viewed, in which case the full understanding of where the tongue must be and of how it must move during the formation and delivery of the sound cannot be conveyed. In addition, a complete viewing of the tongue is impossible, since the human demonstrator's mouth can be opened only to a limited extent and can be viewed from only one direction. Attempts to use certain other model mouths, such as those used in taxidermy and dental work, have met with indifferent success, for they are basically designed only to show teeth and teeth positions, and are not concerned with the subtelties of sound formation and speech. Such models are unsatisfactory, as are the mouths of human demonstrators, because it is impossible to see the position of the tongue from the back, from the top, and from the sides. This limits the ability of the therapist to convey to the patient the identity and function of the different parts of the mouth which cooperate with the tongue in its various positions to make desired sounds.